Diplomats have to put their country's interest above their personal safety, the US ambassador to Iraq said today in defence of a decision to force officials to take up the world's most dangerous foreign posting.

In a new policy announced last week, US foreign service officials will be forced to serve in Iraq or face disciplinary action - including dismissal - in the first order of its kind since the Vietnam war. Diplomats have reacted angrily, with one calling the directive a "potential death sentence".

Ambassador Ryan Crocker insisted diplomats who put their safety before that of the US were "in the wrong line of business".

"As we try to staff the embassy in Iraq, it is good for all our colleagues to remember that we took an oath to serve our nation worldwide when we joined the foreign service, just as the military swore an oath," Mr Crocker told reporters in Dubai.

The union representing diplomats has said security in Iraq is precarious and the completion of a new, heavily fortified embassy compound and living quarters in Baghdad has been dogged by logistical and construction problems.

Mr Crocker said diplomats could not pick and choose their fight.

"It's not for us to decide if we like the policy or if the policy is rightly implemented," he said. "It's for us to go and serve, not to debate the policy, not to agree with it."

The US secretary of state, Condoleezza Rice, yesterday launched a worldwide appeal for volunteers after uproar over the new rules.

She plans to send a cable to all US embassies abroad explaining the decision to launch the largest diplomatic call-up since Vietnam.

The cable would make it clear that foreign service officers are obliged to uphold the oaths they took to carry out the policies of the US government and be available to serve anywhere.

Under the new order, 200 to 300 diplomats have been identified as "prime candidates" for 48 vacancies coming up next year at the US embassy in Baghdad and in Iraqi provinces.

Those notified have 10 days to accept or reject the offer. If too few say yes, some will be ordered to go. Only those with compelling reasons, such as a medical condition or extreme personal hardship, will be exempt from disciplinary action.

Diplomats forced into service in Iraq will receive the same additional hardship pay, vacation time and choice of future assignments as those who have volunteered.

The state department said that since the call-up to fill the 48 vacant Iraq posts was announced last Friday, 15 diplomats had volunteered to work there.

"The most important service for the US at the present time is in the world's hardest places," Mr Crocker said, referring to Iraq, Pakistan and Afghanistan.

At a heated meeting on Wednesday, some diplomats spoke bluntly about the policy to begin "directed assignments" to fill up vacancies in Iraq.

Jack Crotty, a member of the foreign service for 36 years, was among the most vocal, calling the forced deployment to the US embassy in Baghdad or in so-called provincial reconstruction teams in Iraq a "potential death sentence".

Ms Rice sought to dispel the impression that diplomats did not want to serve in Iraq.

"I am very sorry that the recounting of the comments of a few people left the impression that somehow the foreign service does not want to serve in Iraq," she said, on her way to Turkey. "It could not be farther from the truth."

Three foreign service personnel - two diplomatic security agents and one political officer - have been killed in Iraq since the war began in March 2003.